The National Highway Traffic Safety Administration wrapped up a five-year investigation into rusting pipes carrying brake fluid in five million older vehicles.

Those vehicles were never recalled, but owners did often complain about rust causing brake problems.

There were 40 reports of injuries.

The agency determined these brake problems are not the result of a manufacturing or design defect, but rather rust caused by road salt. The recommendation from NHTSA is for vehicle owners to wash the underside of their car several times during and after the winter.

This car wash advisory applies to owners of vehicles from 2007 and older in 20 states, including Minnesota and Wisconsin. Many newer vehicles come with nylon or plastic-coated steel lines, which are not as prone to rusting.

The investigation started in 2010 after a man complained about his 2003 Chevy Silverado.

The NHTSA admitted Thursday it took way too long to simply tell people to wash their cars. They say their Office of Defects Investigation is understaffed, and said in recent years they’ve focused on more serious recall issues that involved multiple crash deaths.

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